This invention concerns an optoelectronic protective device for detecting the presence of unauthorized objects in access or passage openings, such as an opening through a wall.
A variety of such protective devices are known. They are used, for example, to take protective measures when persons approach a danger zone along a monitored path to prevent injuries and/or property damage.
There is a great variety of optoelectronic protective devices, which, based on the individual conditions that are encountered, can be a single-beam light barrier, a multi-beam light grid, a scanner or one of a variety of cameras. These optoelectronic protective devices monitor a line, a surface, or a space with light beams which are directed onto one or more light-sensitive receivers. When an object crosses one or more of such beams, it affects them; that is, it interrupts them, deflects them, weakens them or the like. This is detected by the light-sensitive receiver or receivers. Signals generated by the receiver are then processed in an evaluation unit so that the protective device can provide an appropriate status message, signal or the like.
In this context, the word “light” is not limited to visible light. For purposes of this application, the word “light” refers generally to electromagnetic radiation such as UV-light, IR-light, as well as visible light, which can be used by optoelectronic sensors, as is well known in the art.
A disadvantage of known optoelectronic protective devices is encountered when they have to monitor a passage or access opening because, due to their shape and/or size, they extend significantly into such an opening. This restricts the monitored space or area and can lead to dead zones in the opening where objects cannot be detected. This is particularly problematic for camera-based protective devices, because there will be a dead zone between the control unit and the wall surface behind the unit where objects cannot be seen by the camera